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Numerous plum pox virus (PPV) strain D isolates have been found in geographically distant regions of European Russia and the Crimean peninsula on different stone fruit hosts. Phylogenetic analysis of their partial and complete genomes suggests multiple introductions of PPV-D into Russia. Distinct natural isolates from Prunus tomentosa were found to bear unique amino acid substitutions in the N-terminus of the coat protein (CP) that may contribute to the adaptation of PPV-D to this host. Serological analysis using the PPV-D-specific monoclonal antibody 4DG5 provided further evidence that mutations at positions 58 and 59 of the CP are crucial for antibody binding.

UMR BGPI Equipe 6; Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; The genetic diversity of plum pox virus strain M (PPV-M) was assessed by analyzing 28 isolates collected in 8 European countries. Two genomic fragments spanning the (Cter)P3-6K1-(Nter)CI coding region as well as the full coat protein coding region were sequenced directly from PCR products. Phylogenetic analysis showed that the geographical origin of the collected isolates was clearly associated with two different PPV-M clades. Moreover, the pattern of substitutions in the CP gene shed light on the evolutionary relationships between PPV-M and the recombinant strains PPV-Rec and PPV-T.

International audience; The recent observation of the frequent occurrence of natural recombinant Plum pox virus (PPV) isolates has led to the identification of a distinct PPV subgroup, named PPV-Rec. The diversity, origin and geographical spread of the recombinant PPV isolates belonging to this subgroup remain, however, relatively poorly known. In an effort to further our understanding of these isolates, eight PPV isolates from Serbia, the country from which the first such recombinant (PPV-o6) originated, were characterized. Depending on the genomic region targeted by different typing assays, seven of the eight isolates tested presented discrepancies in their typing behavior. Sequence analysis of the (Cter)NIb-(Nter)CP region confirmed the recombinant nature of these seven isolates which all presented an identical recombination breakpoint identical to previously characterized PPV-Rec isolates. Biological indexing and immunoblot analysis provided indications that asymptomatic infection of the GF305 peach indicator and migration of the coat protein as a double-band in immunoblots may represent conserved and discriminating properties of PPV-Rec isolates. The genetic diversity of PPV-Rec isolates from former Yugoslavia (Serbia, Bosnia and Herzegovina) was estimated to be twice as large as that of the PPV-Rec isolates obtained from all other countries to date (Albania, Bulgaria, Czech republic, Germany, Hungary and Slovakia). These last results are consistent with the hypothesis that former Yugoslavia is the center of dispersion of PPV-Rec. Taken together, the results presented here provide further evidence for the wide distribution and temporal genetic stability of these natural PPV recombinant isolates and provide for the first time a possible scenario for their dispersion throughout central and eastern Europe.

Plum pox virus (PPV) sweet (SwC) and sour (SoC) cherry isolates were the first PPV isolates to be recovered from natural infection in sweet and sour cherry plants, respectively. Their complete nucleotide sequences have been determined finding a deduced genome organisation typical for PPV species. Both genomes are 9795 nucleotides long, excluding the 3' terminal poly(A) tail, and contain an open reading frame of 9432 nt, encoding a polyprotein of 3143 amino acids. The nucleotide and predicted amino acid sequences of PPV-SwC and SoC have been pairwise compared with available sequences of different PPV strains. Although a very high similarity exists between the whole genomes and polyproteins of the two cherry isolates, high levels of divergence have been calculated with sequences of PPV-M, D and EA isolates. In particular, the most considerable divergence has been found in part of 5' non coding region, in regions encoding P1, P3 + 6K1, 6K2 and NIa-VPg proteins as well as in the N-terminal domain of the coat protein. Phylogenetic analysis have been undertaken in order to establish the taxonomic localisation of SwC and SoC isolates within PPV species, showing that they are always clustered together and separated from the rest of PPV strains, being clearly the most distant.

The complete genome sequences of two asparagus virus 1 (AV-1) isolates differing in their ability to cause systemic infection in Nicotiana benthamiana were determined. Their genomes had 9,741 nucleotides excluding the 3′-terminal poly(A) tail, encoded a polyprotein of 3,112 amino acids, and shared 99.6 % nucleotide sequence identity. They differed at 37 nucleotide and 15 amino acid sequence positions (99.5 % identity) scattered over the polyprotein. The closest relatives of AV-1 in amino acid sequence identity were plum pox virus (54 %) and turnip mosaic virus (53 %), corroborating the classification of AV-1 as a member of a distinct species in the genus Potyvirus.

Antisera to the bacterially expressed nonstructural proteins (NSP) HC-Pro, CI, NIa, and NIb and the coat protein (CP) of plum pox potyvirus (PPV) were used for analysing the composition of virus-induced cytoplasmic and nuclear inclusions by electron microscopy. The antisera reacted with NSP and CP of PPV on immunogold-labelled ultrathin sections. Antiserum to CP reacted with virions of seven out of 18 other potyviruses. CP was distributed throughout the cytoplasm of infected cells. Antisera to PPV NSP specifically reacted with virus-specific cytoplasmic and/or nuclear inclusions induced by 17 different potyviruses. NSP were furthermore localized in confined cytoplasmic areas in between complex accumulations of virus-specific inclusions. Cylindrical inclusions induced by the potyviruses were proven to consist of CI protein. Most other cytoplasmic or nuclear inclusions were shown to be composed of two or more NSP. An unexpected composition of virus-induced inclusions was observed for the crystalline nuclear inclusions of tobacco etch virus. Here, in addition to the expected presence of NIa and NIb, HC-Pro could be demonstrated. Furthermore, amorphous cytoplasmic inclusions induced by papaya ringspot virus contained the expected HC-Pro but additionally NIa, NIb and CI. Beet mosaic virus-induced nuclear inclusions ('satellite bodies') contained in their electron-dense matrix NIa, NIb, Hc-Pro and CI and in their lacunae CP in bundles of virion-like filaments. The results indicate that all cytoplasmic or nuclear inclusions of potyviruses have to be regarded as deposition sites of excessively produced viral NSP.

Plum pox virus (PPV) isolates differ by their capsid protein (CP) mobility in SDS-PAGE. These electrophoretic phenotypes are likely to result from post-translational modifications of the CP. We demonstrated that the CP mobility was solely determined by the CP N-terminal region. Sequence comparison pinpointed a possible role of mutations at position 66 in determining the CP phenotype of PPV-Rec isolates. Site-directed mutagenesis of a chimeric clone demonstrated that Gly(66) in the CP resulted in the double-band phenotype, while Arg(66) led to a single-band CP pattern, possibly by preventing the phosphorylation of a nearby Ser residue by steric hindrance.

The genomic sequence of an El Amar isolate of plum pox virus (PPV) from Egypt was determined by sequencing overlapping cDNA fragments. This is the first complete sequence of a member of the El Amar (EA) strain of PPV. The genome consists of 9791 nt, excluding a poly(A) tail at the 3′ terminus. The complete nt sequence of PPV EA is 79–80%, 80%, 77%, and 77% homologous with isolates of strains D/M, Rec (BOR3), C, and W, respectively. The polyprotein identity ranged from 87–91%. Phylogenetic analysis using the complete genome sequence of PPV EA confirmed its strain status. No significant recombination signals were identified using PhylPro and SimPlot scans of the PPV EA sequence, however an interesting recombination signal was identified in the P1/HC-Pro region of PPV W3174.

The complete nucleotide sequence of the NIb coding region of the sour cherry strain of plum pox potyvirus (PPV-SoC) has been determined. It consists of 1554 nucleotides and encodes a putative replicase protein of 518 amino acids. Sequence identity scores between NIb of PPV-SoC and other isolates of PPV are significantly low (c. 78%). Many of the nucleotide substitutions, however, are silent. PPV-SoC differs from isolates of PPV-D, PPV-M and PPV-E1 Amar at multiple amino acid positions that are conserved between the other isolates. The NIb sequence extends the PPV-SoC sequence presently available to 2781 nt from the 3' end (approximately 28% of the genome).

Monoclonal antibodies (MAbs) specific to plum pox virus (PPV) were prepared by fusing myeloma cell lines to spleen cells of mice immunized with purified virus, including virus prepared with protease inhibitors to preserve the integrity of the coat protein (CP). The characterized MAbs could be used in ELISA to differentiate several Mediterranean PPV isolates differing in their geographical origin and CP size. At least seven antigenic sites could be established based on the recognition pattern and competition binding analysis, and the epitopes could be classified in three groups by Western blot analysis of intact and trypsin digested virus particles. By means of electron microscopy the epitopes could be seen to be located on the surface of the virus particles.